I was surprised at how much my random guesses were correct, based on the style of the flags. (Mostly getting it wrong, but maybe 20% success rate)

There is definitely a clustering of design styles. British territories for example tend to have elements of the Union Jack incorporated. Germany, Luxembourg, Italy, that area tend to have more the simple 3 stripe designs.

I found myself occasionally guessing a right answer for flags in regions I knew very little about. I guess that sort of knowledge about design trends seeped in somehow.

I recommend Anki. I've been learning flags (and capitals etc) ~1 year ago. After a few months break I have finished this game with a 97% accuracy (missed 5 countries). I would not get as good without multiple-choice, but it's still nice to see how many flags I did still recall.

Turns out so, so, many random tiny islands that nobody's ever heard of have quite interesting unique flags.